Method of making a partial ester composition of improved stability



METHGD F MAG A PARTHAL ESTER COM- TUSHTIGN 0F IMPROVED STABTLETY Noel H. Knhrt, Rochester, N. Y., assignor to Eastman Kodak Qnmpany, Rochester, N. Y., a corporation of New Jersey Na Drawing. Appiicatian Gctcher 12, 1951, Serial No. 251,133

6 Claims. ct. zen-41a? Fatty acid partial esters of polyhydric alcohols are prepared by reacting fatty material with a polyhydric alcohol in the presence of an ester-interchange catalyst. Fatty materials, and particularly unsaturated fatty materials such as unsaturated triglycerides, fatty acids, and the like, are normally subject to spoilage due to oxidative taxes Patent 0 rancidity. Similarly, the partial ester compositions prepared from such fatty materials are, under ordinary conditions, also readily subject to oxidation and consequent rancidity.

It is accordingly an object of this invention to provide a process of preparing partial ester compositions of improved inherent stability against oxidative rancidity.

Another object of the invention is to provide an esterinterchange process including a method for improving the stability of normally unstable partial esters resulting from such process.

Another object of the invention is to provide an improved method of making monoglyceride compositions stabilized against objectionable oxidation and rancidity.

Another object of the invention is to provide an improved ester-interchange process featured by the use of a material during the process which is effective to stabilize the resulting product against rancidity subsequent to completion of the process and after removal of such stabilizing material.

Another object of the invention is to provide an effective method of processing fatty material normally subject to oxidation to give a product having improved inherent stability against oxidative rancidity.

Another object of the invention is to provide an improved process for preparing partial ester compositions having enhanced stability against oxidative rancidity but free of antioxidants.

Another object of the invention is to provide a new method of making monoglycerides which are more readily stabilized by conventional stabilizing agents than are the monoglycerides produced by the normally employed procedures.

Other objects will be apparent from the description and claims which follow.

These and other objects are attained by means of this invention as described more fully hereinafter with reference to certain preferred embodiments thereof.

Fatty materials such as fatty acids, fatty acid esters, and mixtures of these and similar materials, whether solid or liquid are readily converted to partial esters by reacting such fatty materials with a suitable polyhydric alcohol such as glycerine, in the presence of an esterinterchange catalyst, such as an alkali metal or an alkaline earth soap, such procedures being well known and understood in the art. The triglyceride compositions such as the vegetable oils and animal fats are normally employed in commercial practice for producing monoor diesters, or mixtures of monoor diesters with each other and/or with triglycerides. The fatty materials suitable for use in practicing this invention include any of the natural or synthetic fatty compounds and include solid and liquid fats as well as fatty oils. The fatty compounds employed are preferably those fatty materials having from about 12 to about 20 carbon atoms in the fatty acid chain although fatty acid chains of from about 8 to about 26 carbon atoms are suitable. The fatty acid esters which are suitable include esters of either monohydric or polyhydric alcohols, as, for example, the fatty oils comprising a substantial proportion of mixed triglycerides.

Typical fatty materials which can be treated in accordance with this invention include marine oils such as fish oils, whale oil, and the like; animal fatty materials such as tallow, Wool grease, and the various other animal fats and fatty oils; vegetable oils such as soybean oil, cottonseed oil, coconut oil, peanut oil, and the like, as well as other well-known fatty materials normally subject to oxidativerancidity. Partial esters of such unsaturated fatty acids as linolenic acid, linoleic acid, and the like having improved stability can also be prepared in accordance with this invention.

The alcohol employed in the process embodying this invention can be any of the well-known polyhydric alcohols, and is desirably a lower saturated polyhydric alcohol. Thus, suitable alcohols include the polyhydroxy alkanes such as glycerol, sorbitol, mannitol, and the like; ether alcohols such as diglycerol, polyglycerols, and the like; alkylene glycols such as trimethylene glycol, ethylene glycol, propylene glycol, diethylene glycol, and the like; as well as other well-known polyhydric alcohols.

The catalyst employed in the process embodying the invention can be any of the well-known ester-interchange catalysts and, although the metal compounds such as the alkali and alkaline earth compounds and particularly the bi-valent metal compounds are preferably employed, other suitable catalysts include well-known organic and inorganic acid catalysts such as phosphoric acid, sulfuric acid or similar inorganic acids; substituted inorganic acids such as alkyl sulfuric acid; organic acids such as aryl sulphonic acids and the like; and other acid materials, as well as such other materials as tetramethyl ammonium hydroxide, aluminum chloride, and the like.

I have discovered that, when an ester-interchange reaction is effected between a fatty material and a polyhydric alcohol in a reaction mixture containing an alkali metal salt of ethylene diamine tetra-acetic acid, a partial ester composition having enhanced stability against oxidative rancidity is obtained after separation therefrom of the salt of ethylene diamine tetra-acetic acid. The process embodying the invention is desirably efiected in a reaction mixture containing an excess of the polyhydric alcohol over the amount necessary to react with the fatty material. The ester-interchange reaction is carried out at a temperature substantially above the minimum temperature necessary for formation of the desired partial ester, and best results are obtained at temperatures above C. It is desirable to effect the alcoholysis at a temperature which will give an optimum yield of partial ester in a period of from /2 to 4 hours. In most cases it is desirable to form the partial ester of such materials as soybean oil, cottonseed oil, and the like, at temperatures of from to 300 C., and preferably at about 250 to 260 C.

In carrying out the process embodying the invention, an alkali metal salt of ethylene diamine tetra-acetic acid is incorporated into a reaction mixture comprising the fatty material to be converted and an excess of the desired polyhydric alcohol, maintained in the reaction mixture during the ester-interchange reaction, and thereafter separated from the product resulting from the reaction to give a partial ester composition substantially free of such salt but characterized by enhanced stability against oxidative rancidity. The alkali metal salts of ethylene diamine tetra-acetic acid are preferentially soluble in such polyhydric alcohols as glycerine and the salts can be effectively removed from the partial ester products by allowing the excess polyhydric alcohol to separate from the reaction product upon standing. When a monoester product of high potency is desired, such as a relatively pure monoglyceride product, the monoester can be separated from the reaction product by vacuum distillation.

Any of the alkali metal salts of ethylene diamine tetraacetic acid can be employed in practicing this invention, the sodium and potassium salts being preferred for convenience. The salts may be the di-, tri-, or tetra-metal salts of ethylene diamine tetra-acetic acid. Such salts are readily prepared in accordance with well-known practice as, for example, by adding a concentrated aqueous solution of the appropriate alkali metal hydroxide to a glycerol solution of ethylene diamine tetra-acetic acid, a 5% solution of such salt being conveniently employed. The salt is preferably employed in the ester-interchange process in amounts of from 0.05% to 1% by weight of such salt based on the weight of the reaction mixture, although lesser or greater amounts can be employed depending upon the reactants and reaction conditions.

The partial ester compositions obtained by means of this invention exhibit unusual stability against oxidative rancidity, without the addition of any of the conventional antoxidants, such as propyl gallate, citric acid, hydroquinone, or the like. When such a conventional stabilizer is added to the product obtained by means of this invention, however, the stability of the resulting composition is many times the stability of such compositions prepared by conventional processes and containing a like amount of conventional stabilizer.

In a preferred process embodying the invention, a vegetable oil, such as cottonseed oil, is admixed with glycerine in the proportions of 2.3 moles of 'glycerine per mole of cottonseed oil calculated as triglyceride. To this mixture is added 0.1% by weight of strontium oxide and 0.1% by weight of an alkali metal salt of ethylene diamine tetra-acetic acid. The strontium oxide combines with fatty acids in the oil to form a strontium soap which functions as ester-interchange catalyst in the reaction. The resulting mixture is passed through a pre-heater wherein the temperature is raised to about 225 to 230 C. and the heated mixture is then led into a pot reactor. In the reactor, the mixture is heated to 250 to 260 C. and maintained at that temperature for minutes to cause formation of monoglyceride. During the reaction, the mixture is constantly agitated and water vapor evolved during the reaction is vented from the reactor.

The composition resulting fromthe reaction, consisting primarily of catalyst, unreacted glycerine, and mono-, diand triglycerides, is then led through a cooling coil wherein the temperature of the composition is rapidly reduced to about 100 C. The composition is then allowed to stand without agitation for from 5 minutes to /2 hour whereupon a substantial proportion of the unreacted glycerine containing dissolved therein substantially all of the salt of ethylene diamine tetra-acetic acid separates from the body of the composition and is drawn oif.

The resulting glycerine-depleted composition can thereafter be treated to inactivate the catalyst in accordance with well-known practices and used commercially as a source of partial ester. Desirably, however, the glycerine-depleted composition is subjected to vacuum distillation effective to distill mono-glyceride therefrom and this may be accomplished without first inactivating the catalyst. The separation of monoglyceride is readily effected by means of high vacuum substantially unobstructed path centrifugal distillation or by other suitable thin film distillation at a pressure below about 100 microns. The vacuum distillation is readily effected at temperatures of from to 150 C. and pressures of 10 to 300 microns.

The enhanced inherent stability of partial ester compositions prepared in accordance with this invention is illustrated by the following examples of specific embodiments of the invention. The stability of the partial ester composition was determined in each instance by an accelerated stability test wherein the partial ester composition was heated at 97 C. with air blowing through the sample. The peroxide value of the sample was checked periodically by chemical analysis, the development of a peroxide value of. 20 in 3 hours being considered the minimum stability for commercial usage.

Example 1 A. reaction mixture was prepared consisting of cottonsee-:1 oil, giycerine amounting to a 40% excess over the amount required to react with the cottonseed oil, and 0.1 of strontium hydroxide to act as ester-interchange catalyst and 0.1% of the disodium salt of ethylene diamine tetra-acetic acid based on the weight of oil and glycerine. The reaction mixture was heated at 250 C. for 30 minutes during which time the mixture was constantly agitated and evolved water vapor was continuously withdrawn. The reaction mixture was then cooled to 100 C. and allowed to stand for 20 minutes. Upon star the unreacted glycerine containing the salt of ethyl ...e diamine tetra-acetic acid separated from the composition resulting from the reaction and was drawn oil. The resulting glycerine-depleted composition was then subjected to vacuum distillation in a high vacuum centrifugal still at a temperature of about C. and a pressure of 20 microns. A distillate consisting of more than 90% of monoglyceride was obtained thereby. This monoglyceride product was then subjected to the accelerated stability test and the peroxide value checked periodically. The product had a peroxide value of 7 at the. end of 1 hour, a peroxide value of 11 at the end of 3 hours, and a peroxide value of 19 at the end of 5 /2 hours.

A monoglyceride composition was prepared in similar fashion without the use of a salt of ethylene diamine tetraacetic acid in the reaction mixture. This control sample had a peroxide value of 25 in 2 hours. A similar monoglyceride composition prepared using the free acid, ethylene diamine tetra-acetic acid, had a peroxide value of 18 in 2 hours and more than 20 in 3 hours. Thus, the monoglyceride composition prepared in accordance with this invention had an improved inherent stability of more than 100% over the composition prepared by conventional processes and that prepared using free ethylene diamine tetra-acetic acid.

Example 2 A monoglyceride composition was prepared in similar fashion using 0.1% of the tetra-sodium salt of ethylene diamine tetra-acetic acid in the reaction mixture. After separation of the tetra-sodium salt from the reaction product, the monoglyceride product had a peroxide value of 10 after 3 hours in the accelerated stability test and a peroxide value of 15 at the end of 5 hours.

Example 3 A cottonseed oil monoglyceride composition was prepared by reacting cottonseed oil with glycerine in the presence of 0.3% of the tetra-sodium salt of ethylene diamine tetra-acetic acid. The monoglyceride composition obtained by vacuum distillation of the reaction prod not had a peroxide value of less than 20 at the end of 3 hours under the accelerated oxidizing conditions described hereinabove.

Example 4 The partial ester compositions prepared in accordance with this invention not only exhibit increased inherent stability without added antioxidants, but also exhibit a much improved stability when stabilized by the addition of conventional anti-oxidants. Thus, a monoglyceride composition prepared in accordance with conventional processes was stabilized by the addition of 0.15% of butylated hydroxy anisole and 0.5% of propyl gallate. The resulting composition had a stability of hours under the accelerated oxidizing conditions. A monoglyceride composition prepared in accordance with this invention employing 0.3% of the tetra-sodium salt of ethylene diamine tetra-acetic acid in the reaction mixture showed a stability of 85 hours when mixed with the same antioxidants in the same proportions.

Similar results are obtained with other partial ester compositions prepared from any of the fatty materials normally subject to oxidative rancidity using these or other alkali metal salts of ethylene diamine tetra-acetic acid in the reaction mixture.

Thus, by means of this invention, partial ester compositions of greatly enhanced inherent stability against oxidative rancidity are readily obtained. The compositions can be prepared using conventional equipment and without extensive revision of conventional manufacturing operations. The alkali metal salts of ethylene diamine tetra-acetic acid are readily separated from the desired partial ester composition without the necessity of laborious purifications, and such salts are available for reuse.

The invention has been described in considerable detail with reference to certain preferred embodiments thereof, but it will be understood that variations and modifications can be effected without departing from the spirit and scope of the invention as described hereinabove and as defined in the appended claims.

I claim:

1. The process of preparing a partial ester composition of improved inherent stability against rancidity which comprises providing a reaction mixture containing a fatty material normally subjectto oxidative rancidity, an excess of a polyhydric alcohol, and an alkali metal salt of ethylene diamine tetra-acetic acid, reacting said fatty material and said polyhydric alcohol in said reaction mixture at a temperature of at least 100 C.

and thereby forming a reaction product containing a substantial amount of fatty acid partial ester of said polyhydric alcohol in admixture with unreacted polyhydric alcohol and said alkali metal salt of ethylene diamine tertiacetic acid, separating from said reaction product unreacted polyhydric alcohol having dissolved therein substantially all of said salt of ethylene diamine tetraacetic acid and recovering a fatty acid partial ester composition having improved inherent stability against oxi dative rancidity but being substantially free of said salt of ethylene diamine tetra-acetic acid.

2. In the process of making a composition containing a fatty acid partial ester of a polyhydric alcohol by effecting ester-interchange between a fatty material I101: mally subject to oxidative rancidity and a polyhydric alcohol in a reaction mixture containing an ester-interchange catalyst, the method of enhancing the inherent stability of said composition against oxidative rancidity which comprises incorporating an alkali metal salt of ethylene diamine tetra-acetic acid in said reaction mixture, maintaining said salt of ethylene diamine tetraacetic acid in said reaction mixture While effecting esterinterchange between said fatty material and said polyhydric alcohol at a temperature of at least 100 C., and separating substantially all of said salt of ethylene diamine tetra-acetic acid from the composition obtained by effecting said ester-interchange.

3. The method of making a composition of improved inherent stability against oxidative rancidity and containing a substantial amount of a monoglyceride, which method comprises reacting a fatty material normally subject to oxidative rancidity and glycerine in a reaction mixture containing an alkali metal salt of ethylene diamine tetra-acetic acid, said reacting being effected at a temperature of at least C. and thereby forming a reaction product containing a substantial amount of monoglyceride, and separating substantially all of said salt of ethylene diamine tetra-acetic acid from said reaction product and recovering a composition containing said monoglyceride and substantially free of said salt of ethylene diamine tetra-acetic acid, said composition being characterized by enhanced stability against oxidative rancidity.

4. The method of making a monoglyceride composition of improved inherent stability against oxidative rancidity which comprises reacting a fatty material normally subject to oxidative rancidity with an excess of glycerine in a reaction mixture containing a sodium salt of ethylene diamine tetra-acetic acid, said reacting being effected at a temperature above 100 C. and being efiective to form a reaction product containing a substantial amount of monoglyceride in admixture with unreacted glycerine and said salt of ethylene diamine tetra-acetic acid, separating said unreacted glycerine and said salt of ethylene diamine tetra-acetic acid from said reaction product and recovering a monoglyceride composition substantially free of said sodium salt of ethylene diamine tetra-acetic acid and having enhanced inherent stability against oxidative rancidity.

5. The method of making a monoglyceride composition of improved inherent stability against oxidative rancidity which comprises elfecting ester-interchange between a triglyceride normally subject to oxidative rancidity and an excess of glycerine at a temperature above 100 C. and in the. presence of a sodium salt of ethylene diamine tetra-acetic acid and thereby forming a reaction product comprising a substantial amount of monoglyceride in admixture with unreacted glycerine and said salt of ethylene diamine tetra-acetic acid, separating from said reaction product said unreacted glycerine containing dissolved therein said salt of ethylene diamine tetraacetic acid, and vacuum distilling monoglyceride from the residue obtained from said separating and thereby obtaining a monoglyceride composition of improved inherent stability against oxidative rancidity but substantially free of said salt of ethylene diamine tetra-acetic acid.

6. The method of making a monoglyceride composition of improved inherent stability against oxidative rancidity which comprises reacting a vegetable oil with an excess of glycerine in the presence of a sodium salt of ethylene diamine tetra-acetic acid and at a temperature of at least 100 C. and thereby forming a reaction product containing a substantial amount of monoglyceride, separating excess glycerine from said reaction product by phase separation, said excess glycerine containing said salt of ethylene diamine tetra-acetic acid dissolved therein, and vacuum distilling monoglyceride from the resulting glycerine-impoverished reaction product and thereby obtaining a stabilized monoglyceride product substantially free of said salt.

References Cited in the file of this patent UNITED STATES PATENTS 2,371,623 Henderson Mar. 20, 1945 2,442,534 Eckey June 1, 1948 2,463,015 Bersworth Mar. 1, 1949 

1. THE PROCESS OF PREPARING A PARTIAL ESTER COMPOSITION OF IMPROVED INHERENT STABILITY AGAINST RANCIDITY WHICH COMPRISES PROVIDING A REACTION MIXTURE CONTAINING A FATTY MATERIAL NORMALLY SUBJECT TO OXIDATIVE RANCIDITY, AN EXCESS OF A POLYHYDRIC ALCOHOL, AND AN ALKALI METAL SALT OF ETHYLENE DIAMINE TETRA-ACETIC ACID, REACTING SAID FATTY MATERIAL AND SAID POLYHYDRIC ALCOHOL IN SAID REACTION MIXTURE AT A TEMPERATURE OF AT LEAST 100* C. AND THEREBY FORMING A REACTION PRODUCT CONTAINING A SUBSTANTIAL AMOUNT OF FATTY ACID PARTIAL ESTER OF SAID POLYHYDRIC ALCOHOL IN ADMIXTURE WITH UNREACTED POLYHYDRIC ALCOHOL AND SAID ALKALI METAL SALT OF ETHYLENE DIAMINE TERTAACETIC ACID, SEPARATING FROM SAID REACTION PRODUCT UNREACTED POLYHYDRIC ALCOHOL HAVING DISSOLVED THEREIN SUBSTANTIALLY ALL OF SAID SALT OF ETHYLENE DIAMINE TETRAACETIC ACID AND RECOVERING A FATTY ACID PARTIAL ESTER COMPOSITION HAVING IMPROVED INHERENT STABILITY AGAINST OXIDATIVE RANCIDITY BUT BEING SUBSTANTIALLY FREE OF SAID SALT OF ETHYLENE DIAMINE TETRA-ACETIC ACID. 